Ethereum: What prevents the Solidity compiler from optimizing `address(this).balance` for `selfbalance()`?

The Optimizer’s Dilemma: Unpacking Ethereum’s Optimization Mechanisms

In this article, we’ll delve into the world of the Ethereum optimizer and explore why address(this).balance doesn’t always optimize to self.balance().

Background to Solidity Compilers

Ethereum’s Solidity compiler is a critical component that translates high-level code written in Solidity (a programming language used to build decentralized applications) into low-level bytecode. This process involves a series of optimization steps aimed at improving the performance, readability, and maintainability of the code.

Optimizer: A Key Component

The Ethereum Virtual Machine (EVM) has an optimizer that runs on top of the Solidity compiler. Its primary function is to reduce the size and complexity of the bytecode produced by the compiler while maintaining or even increasing the accuracy of the optimized code. The optimizer considers various factors, including:

• Gas Cost: Higher gas costs can drive optimization decisions.

• Code Length: Longer codebases are more likely to be optimized for performance.

• Instruction Set Usage: Frequent use of complex instructions may require optimization.

Why address(this).balance is not always optimized

Consider an example:

pragma strength ^ 0,8,0;
contract MyContract {
function balance() public view returns (uint256) {
return address(this).balance;
}
// We implement a simple optimization: when self.balance() is called,
// we update the balance without using address(this).balance.
function updateBalance() public {
uint256 newBalance = self.balance();
address(this).balance = 0; // This line can be optimized
}
}

In this case, the optimizer will probably decide to optimize the line address(this).balance = 0 when calling self.balance(). This is because updating a local variable without using its original value can reduce gas consumption.

Difference between self.balance() and address(this).balance()

While it may seem that self.balance() and address(this).balance() are equivalent, there is one important difference:

• self.balance() returns the balance of the current contract instance.

• address(this).balance() returns the balance of the current contract address.

This means that when calling updateBalance(), we want to update a local variable on the current contract instance (self), rather than modify the global state. By using address(this).balance(), we ensure that the optimization is applied correctly, as it refers to a local value instead of a global one.

Conclusion

In conclusion, while the Solidity compiler and its optimizer try to optimize code for performance, there are scenarios where optimizations may not always apply or may even be intentionally circumvented. The key takeaway from this example is that the difference between self.balance() and address(this).balance() lies in their referential semantics, which can affect optimization decisions.

As a developer working with Ethereum’s EVM, understanding these subtleties will help you write more efficient, readable, and maintainable code while minimizing gas consumption.